Conventional transmissions are configured to receive power from an engine via an input shaft thereof and transmit the engine power from an output shaft thereof to a crawler traveling unit for driving the crawler traveling unit. A typical example of such conventional transmissions is disclosed in Japanese Patent Laid-open Publication (JP-A) No. 63-223207.
The disclosed transmission has an input shaft adapted to be connected to an engine, a series of shift gears connected in driven relation to the input shaft, an output shaft connected in driven relation to a final shift gear of the series of shift gears, a clutch coupled with the output shaft, and a reduction gear connected to the clutch. The reduction gear is mounted to a drive shaft connected to a crawler traveling unit. The transmission includes a fixed lower transmission part including the shift gears, and a movable upper transmission part including the clutch and the reduction gear. The upper and lower transmission parts are connected together via the drive shaft. The upper and lower transmission parts are manufactured as structurally independent separate units and, when they are assembled together, a longitudinal part of the drive shaft is exposed between the upper and lower transmission parts or units. Each of the upper and lower transmission units requires a seal member for hermetically holding a lubricating oil within the respective transmission unit and a breather chamber and a breather passage that are provided for ventilation in a housing of the respective transmission unit.
The conventional transmission of the foregoing construction is relatively large in size and requires a relatively large number of components which will render the transmission complicated in construction and costly to manufacture. Furthermore, due to the presence of the exposed longitudinal portion, the drive shaft rusts easily.
With the foregoing drawbacks of the prior art in view, an object of the present invention is to provide a transmission, which is compact in size and requires a relatively small number of components, making the transmission simple in construction and less costly to manufacture.